1. Field of the Invention
This invention pertains to the recovery of oil from a subterranean, viscous oil-containing formation utilizing an improved in-situ combustion process.
2. Background of the Invention
In-situ combustion is a common method for recovering viscous crudes or tar sands. The use of high purity oxygen in place of air significantly improves the performance of the in-situ combustion process. The injection of oxygen into a wellbore, however, presents significant hazards and requires safety precautions. Previous work in this regard includes the injection of O.sub.2 through a bottom water zone, as disclosed in U.S. Pat. No. 3,208,519, and the initiation of combustion with air followed by oxygen as disclosed in an article by G. Pusch, Erdol und Kohle-Erdgas-Petrochemie combined with Brennstoff-Chemie, Vol. 30, No. 1, Jan. 1977, pp. 13-25. All these methods use air to establish gas flow. However, it has been found that injection of air increases the viscosity of the oil by 100 times when the oil is contacted by air for two days at 210.degree. F. This increase in viscosity is detrimental to the recovery process. In addition, the inert gaseous nitrogen in the air injected tends to reduce the effective permeability for oil in the reservoir.
My invention proposes a method to initiate the in-situ combustion operation initially using a combustion supporting gas comprising a mixture of essentially pure oxygen and carbon dioxide followed by the use of essentially pure oxygen that eliminates the problem of increasing the viscosity of the oil in the formation using conventional combustion supporting gases such as air, air enriched with oxygen, or oxygen.